Rheostat.



L. L. TATUM.

RHEOSTAT.

APPLICATION FILED DEG. 7, 190a.

Patented Sept. 29, 1914.

8 SHEETS-SHEET 2.

UNITED STATES PATENT OFFICE.

LEWIS L. TATUM, OF MILWAUKEE, WISCONSIN, ASSIGNOR TO THE CUTLER-HAMMER MFG. 00., F MILWAUKEE, WISCONSIN, A CORPORATION OF \HISGONSIN.

annosrn'r.

Specification of Letters Patent. Patented Sept, 29 1914,.

Application filed December 7, 1908. Serial No. 466,351.

To' all whom it may concern Be it known that I, LEWIS L. TA'rUM, a citizen of the United States, resldlng at Milwaukee, in the county of Milwaukee and State of Wisconsin, have invented new and useful Improvements in Rheo-stats, of WlllCh the following is a full, clear, conclse, and exact description, reference being had to the accompanying drawing, forming a part of this specification. I

IMy invention relates to improvements in rheostats, and it is my object to provlde a device of very simple construction which will meet varying conditions of servlce.

' Other objectsand advantages of the device will be hereinafter made clearly apparent.

- My invention may assume many various forms. In the accompanying drawings I have shown one form which has been worked out in practice.

In said drawings,Figure 1 is a vertical sectional view, as seen on line 11, Fig. 2, looking in the direction of arrows; Fig 2 is a vertical sectional view, as seen on 11118 2-2, Fig. 1, looking in the direction of arrows; Fig. 3 is a horizontal sectional view, as seen on line 33, Fig. 1, looking in the direction of arrows; Fig. 4 is a detail plan view' of a portion of one of the grids, parts of the reinforcing member being shown in section; Fig. 5 is a sectional view through one of the grids, and its reinforcing member, as seen on line 5-5, Fig. 4:; Fig. 6 is a central, longitudinal, sectional view through the end of the contact arm and the two adjacent grids, and Fig. 7 is a sectional view, as seen on line 77, Fig. 6.

I provide a suitable frame for the entire structure, comprising a pair of supporting members 1 and 2, which are preferably made of angle iron and bent into substantially U-shaped form. Plates 3 and 4 are secured to said members to form the front and back of the frame. The ends of the U-shaped members 1 and 2 are preferably extended below the plates 3 and 4 to provide supporting standards for the frame.

A top 5 and ends 6 are preferably formed of a single piece of foraminous material. The

holes in the top and ends are to provide proper ventilation. The parts of the frame are secured together into a rigid structure by means of screws 7 though other securing 55 means may be employed. Handles 8 by means of which the entire structure may be I moved, are secured to the ends 6.

The resistance units 9 if my device are preferably of the grid type formed of cast lI'OIl, or other deslred resistance material. These grids are cast in substantially rectangular form with slots 10 extending alternately from opposite sides, whereby a resistance strlp, occupying a minimum space, is secured. The end portions of the grid are formed with enlarged bosses. 11. The grids are adapted to be supported in the frame on rods 13, which carry insulating sleeves 14. The grids are assembled as follows: The rods and Sleeves are disposed through the bosses at the end of the grids and have washers 15 and 16,,formed of insulating and conducting material respectively, interposed between adjoiningfbosses. Said insulating and conducting Washers are disposed in staggered relation at opposite ends of the grids, so that the several grids are serially arranged and form a continuous electrical path for the current. The rods are screwthreaded at each end to receive nuts 17, which secure the grids in assembled relation, and additional nuts 18 by means of which the rods, and grids carried thereby, aresecured 'to the plates 3 and 4 of the frame.

The ends of the convolutions, formed by the slots 10, are provided with enlarged portions 19, over which I' secure a remforcing strip of metal 20. A strip of nonconducting material 21, such as asbestos, is interposed between the grid and the metal strip to prevent short circuits between said grids and the reinforcing strips'. By means of this construction the grids are greatly strengthened and enabled to withstand severe shocks due to rough handling.

In practice it is often found ex edient to use a fixed resistance and a varia le resistance. In the drawing I have shown a fixed resistance comprising six grids, though this number may be varied to suit varying conditions. The fixed and variable resistances are designated by a and b respectively. The variable resistance is shown as consisting of a pair of grids b which are provided with a series of raised contact surfaces 22, formed near the lower ends of the convolutions. Said raised contact surfaces are concentrically arran ed with regard to a rod 23, pivotally mounted in the. upper ends of the plates 3 and 4. The plates 3 and 4 are provided with collars 24 fastened on one face, through which the rod 23 extends, longitudinal movement of said rod being prevented by collars 25, fastened thereon, adjacent to said plates. A contact carrying arm 26 is secured to the rod 23, preferably by means of a taper-pin, and is adapted to extend between the adjoining faces of the grids forming the variable resistance 7). The extent of movement of said arm is limited in either direction by lugs 27, formed thereon, which are adapted to engage an abutment plate 28 secured to the member 2 of the frame.- The arm 26 is provided with an opening near its lower end, in which an insulating bushing 29 is secured. The

bushing 29 may be secured in place by means of screws 30, which are locked in adjusted position by nuts 31. The bushing extends beyond the faces of the arm and prevents said arm from making contact with the grid at any time. Loosely mounted in the insulating bushing 29 is a contact comprising a pair of hollow members 32 and 33.

The member 33 is provided with a reduced portion 34, which extends into the member 32. The reduced portion is provided with an annular groove 35 in which is disposed an expansible spring member 36, which is adapted to bear against the inner wall of the member 32 and thus insure proper electrical connection between the members 32 and 33. A compression spring 37 is disposed within the openings of the spring 37, by the clampin plates 38 and 39. Said plates engage the ower ends of said grids, and are secured in adjusted position by means of screws or bolts 40.

In the drawing I have shown a pair of terminals 41, formed integrally with two of the grids, though I may form terminals on all of the grids whereby the fixed resistance may be varied to suit varying conditions of service. I provide a handle 42 secured to one end of the rod 23, by means of which the contact carried by the arm 26 may be moved as desired over the raised contact surfaces 22 on the grids. By moving the arm 26, the contact carried thereby is brought into engagement-with different contact surfaces and a larger or less number of convolutions of the grids forming the variable resistanceare included in circuit, thus varying the total resistance in circuit.

While I have described the variable resistance grids as being formed with raised contact surfaces, as by such a construction the temperature of the grids at the point of contact is reduced, it will beunderstood voltage, and that some means to diminish the flow must be utilized. To this end my device is applicable. In such cases a high resistance, which will reduce the current to approximately the desired degree, and an additional resistance, which may be varied by means .of the rheostat arm, to bring the current to the desired degree, are utilized.

By the construction herein set forth, it will beseen that the contact carrying arm is dead, and that the grids and the contact are the only parts of the device which carry current. It will also be seen that the contact carrying arm 26 does not necessarily. have to move parallel with the grids, as the members 32 and 33 will be free to move through the bushing to compensate for any lateral movement of the arm. It will further be seen that the entire structure is absolutely fireproof. I

-Having thus described my invention, what I claim as new and desire to secure by Letters Patent, is

l. The combination witlra grid resistance, comprising a series of convolutions, of a movable contact element adapted to engage said convolutions, said convolutions having raised contact surfaces.

2. In a variable resistance device, in combination, a pair of electrically connected resistance grids arranged with adjoiningsurfaces, and a contact element adapted to simultaneously engage and be moved over the adjoining surfaces of said grids.

3. In a variable resistance device, in combination, a pair of resistance grids formed of a series of convolutions, and a contact member movable between said grids and adapted to simultaneously engage a convolution of each grid.

4:. In a variable resistance device, in C0111- bination, a pair of resistance grids, and a movable element adapted to simultaneously engage and vary said grids.

5. In a variable resistance device, in co1nbination, a pair of resistance grids, and a movable element adapted to sinniltaneously engage said grids to short-circuit portions of the same.

6. In a variable resistance device, in combination, a pair of resistance grids, and a movable element adapted to simultaneously engage and electrically connect said resistance units at different points.

7 In a variable resistance device, in combination, a pair of grids comprising a series of convolutions, the ends of the convolutions being enlarged, an insulating and a reinforcing strip disposed over the enlarged ends of said convolutions, clamping mem- "bers for maintaining said grids in spaced loosely mounted in said bushing adapted to engage the adjoining faces. of the pair of grids. V i

10. Ina rheostat, in combination, a plurality of electrically connected resistance I rids, a pair of said grids having adjoining aces, a contact arm movable between said adjoining pair of grids, an insulating bushing carried by said arm, and a contact loosely mounted in said bushing comprising a pair of hollow telescoping members, and a compression spring disposed in said members adapted to insure the engagement of the contact with the adjoining faces of the grids.

11. In a rheostat, in combination, a frame, a plurality of resistance grids arranged in said frame and insulated therefrom, an arm pivotally mounted in said frame and extending between a pair of said grids, and a contact member carried by and insulated from said arm, adapted to simultaneously engtge and electrically connect said pair of 1 s. l2. A resistance grid comprising a con-. tinuous convoluted resistance element having a plurality of integral re-inforced contact surfaces thereon.

13. A resistance grid havin of integral raised contact sur aces thereon.

14. A resistance grid comprising a continuous convoluted resistance element, the convolutions thereof lying in substantially the same plane and certain of said convolutions having contact port-ions projecting substantially at right. angles to the plane. of said convolutions.

15. A unitary resistance grid'comprising a series of convolutions, said grid having a series of raised contact surfaces on its convolutions arranged in the form of an arc.

16. In a variable resistance device, in

combination, a pair of resistance grids comprising a series of, convolutions, the ends of the. convolutions being enlarged, an insulating and a reinforcing strip disposed over said enlarged portions, means engaging the a plurality reinforcing strips on adjoining ends of said grids adapted to hold the convolutions of said grids in alinement, and a contact member disposed between said grids and adapted to be moved to electrically connect sald grids at different points.

17. In a variable resistance device, 1n combination, a supporting frame, a plurality of grids formed of convolutions and arranged in said frame, a plurality of raised contact surfaces on said convolutions, an. arm pivotally mounted in said frame and movable between a pair of grids, an insulating bushing carried by said arm, and an expansible.

contact in said bushing adapted to simultaneously engage a contact surface on each of said pair of grids.

18. In a variable resistance device, in combination, a frame, a pair of grid resistances mounted therein and electrically connected, said grids comprising a series of convolutions, and means adapted to be moved into engagement with adjoining convolutions to electrically connect said grids at different desired points.

19. In a variable resistance device, in combination, a frame, a pair of grid resistances mounted therein, said grids comprising a series of convolutions, a pivoted arm extending between said grids, and a contactcarried by said arm adapted to engage a convolution of each of said pair of grids.

20.-In a variable resistance device, in combination, a pair of ids each comprising a series of convo utions, said grids being arranged with adjoining faces, means for rigidly holding said grids in alinement, and adjustable means adapted to engage a convolution of each grid to electrically connect said grids at different points.

21. In a variable resistance device, in

combination, a frame a pair of grids arranged therein with adjoining faces, each grid comprising a series 'of convolutions, means for holding the convolutions of said grids in spaced relation, a contact arm pivoted in said frame fiand extending between the adjoining faces of said grids, said contact arm being movable over said convolutions to electrically connect said grids at different oints.

22.- A r costat comprising a plurality of resistance units arranged side by side and electrically connected, and a controlling member directly engaging certain of said units and movable to vary the resistance thereof in small degrees, the remaining units forming in a fixed resistance.

23. A rheostat comprising aplurality of resistance units arranged parallel 'to one another and electrically connected, and a controlling member disposed between two adjacent units and engaging contacts provided thereon, said controlling elementv being movable to vary theresistance of said therein and electrically connected, and a controlling member arran ed between two adjacent units and direct y engaging the Copies of this patent may be obtained for convolutions thereof, said controlling member being adapted to electrically connect different convolutions of one unit to corre' sponding convolutions of-the other, thereby short-circuiting other convolutions to produce fine varlations in resistance, the re maining units forming a fixed resistance.

In witness whereof, I have hereunto subscribed my name in the presence of two witnesses.

LEWIS L. TATUM. Witnesses:

S. W. FITZGERALD, FRANK H. HUBBARD.

the cents each, by addressing the Commissioner of lat'cntl. Washington, D. 3." 

